1. Field of the Invention
The present invention relates to an image compression method, and more particularly, to an image compression method for video decoding based on a motion compensation such as MPEG-2 by using an image compression algorithm in which an image characteristic is differentiated on the basis of a difference between adjacent pels and finally classified by image types by using image characteristic information, and a suitable code word is assigned to each image type, thereby executing an image compression.
2. Description of the Background Art
Decoding of a video bit stream such as MPEG-2 requires lots of memory to compensate the motion from the reference picture. Thus, a classified differential coding (CDC), a simple image compression algorithm, has been proposed as a way to reduce the frame buffer memory.
Generally, motion estimation (ME) along with the inverse discrete cosine transform (IDCT) has gained wide acceptance as a powerful technique to compress the motion video.
In order to decode the MPEG-2 video, at least two pictures need to be stored as the reference frame for the motion compensation (MC). Roughly, it amounts to 8.9 M bytes in the high definition (HD) decoding. Therefore, implementation of an MPEG-2 video decoder requires an image compression algorithm which could enable the developers to use less memory without sacrificing the decoded picture quality.
In the image compression method, simplification of computation and efficiency and easiness in data access are critical.
Conventionally, as the image compression method, a tree-structure vector quantization (TSVQ) technique, a pyramid vector quantization(PVQ) technique or a variable length coding(VLC) technique have been proposed.
However, the TSVQ technique disadvantageously includes a complicate operation such as codebook search. The PVQ requires a complicate arithmetical operation such as division, which causes more hardware, much execution time and design effort. In case of the VLC, its random accessibility is not good. Thus, these techniques fail to meet the need of simplification of computation and efficiency and easiness in data access.
Therefore, an object of the present invention is to provide an image compression method-which is capable of reducing computational complexity for image compression coding and of satisfying a random accessibility by providing a CDC (classified differential coding) algorithm having a high random accessibility and a low hardware complexity in video decoding based on motion compensation such as MPEG-2.
In the present invention, in order to compress an image, a difference between adjacent two pels is computed and an image region is divided into a mild region, an edge region and a random pattern region for which different code words are assigned. Especially, a bundle is defined by setting up a size of a pel block, an image characteristic is determined by searching values between adjacent and neighboring pels and its variation pattern, and a corresponding region suitable to each image characteristic is assigned with a suitable code word by bit allocation, thereby compressing an image.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an image compression method including the steps of: determining an image bundle type; and giving a cord word to the determined image bundle type by an appropriate bit allocation.
In the image compression method of the present invention, in the step of determining an image bundle type, an image is divided into a mile region and an edge region on the basis of visual characteristics (factors that affects an image recognition) of human beings, and characteristic of the image is finally determined on the basis of a difference between adjacent or neighboring pels of each region and its variation pattern, to thereby assigning an suitable code word corresponding to the variation pattern of each pel by a bit allocation.